I can’t tell if i’m just lazy or if i have adhd

all my life i’ve struggled with school and i’ve been told i’m “so smart” and would have “so much potential” if only i “applied myself” but the problem is, i don’t know how. I can never focus on anything, lectures, tests, homework, you name it. even trying to focus is exhausting. i know that i have responsibilities and i understand the consequences of not doing them, and trust me i want to do them. but it’s like i have some sort of mental block. my brain literally won’t let me focus on anything i need to get done. My grades are awful, my entire life is a mess, im even losing sleep over it. i’ve has mental breakdowns over not being able to focus just because it is so hard and i don’t understand why i can’t just do what i need to do like everyone else in the world. i talked to my guidance counselor and they suggested i get tested but all my life my teachers never acted like there was a real problem, they just treated me like a lazy student who doesn’t care about school so it’s somewhat ingrained in me that its all it is. but do you think that this could be adhd?